Multiple magnetic heads



Jan. 19, 1965 YVES-JEAN F. BRETTE 3,166,740

MULTIPLE MAGNETIC HEADS 3 Sheets-Sheet 1 Filed D60. 30, 1959 Jan. 19, 1965 YVES-JEAN F. BRETTE 3,166,740

MULTIPLE MAGNETIC HEADS 3 Sheets-Sheet 2 Filed Dec. 30, 1959 llb Jan. 19, 1965 YVES-JEAN F. BRETTE 3,166,740

MULTIPLE MAGNETIC HEADS Filed Dec. 30, 1959 3 Sheets-Sheet 3 of adjacent-cores are overlapping'each other. .7

United States Patent Ofitice 3,166,74s Patented Jan. 19, 1-965 MULTIPLE MAGNETIC HEADS Yves-Jean Francois Brette, Sevres, France, assignor to Compagnie des Machines Bull (Socit. Anonyme),

Paris, France Filed Dec. 30, 195?, Ser. No. 862,852 Claims priority, application France, Jan. -6, 1959, 783,351, Patent 1,213,217 3 Claims. (Cl. 3401-'74.1)

This invention relates to multiple magnetic heads comprising transducer elements juxtaposed in such manner that their air gaps are situated in proximity to one another along a line.

Known magnetic heads of this type are used for the simultaneous recording of signals at closely spaced points on a magnetic recording medium and for the simultaneous restoration of signals thus recorded. In order to reduce the crosstalk which then occurs between the transducer elements, the shielding means having various compositions and various forms have been use d in the construction of such heads. ,Screens consisting of magnetic substance which are disposed between adjacent transducer elements to avoid crosstalk, however, constituteconsiderable leak age permeances, and this is generally accompanied by a reduction in the useful flux at-recording or atreading. Y A gap is then provided between these screens and the adjacent transducers. This gap nevertheless remains smaller than one half of the. alreadyreduced gap separating two adjacent transducers. .In addition, such screens, as also the otherhshielding elements, become ineffective when their thickness is reduced in; orderto reduce the gaps between the transducers, andthey are the more difiicult to prepare and tozposi-tign as theirdimensions are smaller.

One'object of the invention is to obviate the aforesaid disadvantages. 7 j a I a Accordingly, theinvention provides amultiple magnetic head comprising ,--a plurality of flat electromagnetictransducers, each including a magnetic core with pole ends which are spaced from each other to provide-an airgap, a first leg carrying a coil and terminating in one of said pole ends, and a second leg terminating in the other of said poleends, said transducers being assembled side by ,side with their 'air gaps in alignment within a common plane and with'coils' of adjacent transducers on opposite sides of said common plane, the second legof the core of each transducer lying along the second leg of theadjacent cores and being so formed that largeportions of the second leg- By. virtue 'ofthe invention it is "possible to construct a'form and an arrangement of the magnetic circuits such that some-parts of the magnetic circuits of each transducer perform a magnetic shielding function with respect to the adjacent'tr'ansducers, so that thle insertion of additional howjit may be carried' intopffect, the same willnow be multiple magnetic heads whichare; substantia1ly.smaller thanthose' heretofore provided. This may. be effected by described, by way of example, with reference to the ac, companying drawings, in which:

FIGURE 1 is an elevational view of a transducer element for a multiple magnetic head according to the invention,

FIGURE 2 is an exploded perspective View of a multiple magnetic head according to an embodiment of the invention, comprising three transducer elements,

FIGURE 3 is a perspective view of the multiple head showing the transducer elements assembled together,

FIGURE 4 is an elevational view of the multiple head illustrated in FIGURES 2 and3,

FIGURE 5 is an underneath plan view of said head,

FIGURE 6 is a view similar to that of FIGURE 4, showing elements which are employed in the operation of multiple heads according to the invention,

FIGURES 7, 8, 9 and 10 are views similar to FIGURE 4, showing further embodiments of the invention,-and

FIGURE 11 is an underneathplan view showing a modified constructionalform of the multiple head.

FIGURE 1 illustrates a transducer element 10, such "as is employed with other similar transducer elements in the formation of a multiple head according to a first embodiment of the invention. i I

' The transducer element It] comprises essentially a mag-l netie circuit having an air gap and an electric winding.

The magnetic circuit consists of a rectangular plate 1-1.

of magnetic material formed with a triangular recess-12 1 10 2, ltlhand 10c forming aimultiple head are of like;

which the windings are'mounted are situated alternately 1 I to the right and to the left of the uprights 14a, 14b, 14a,

The said transducer element's form, when assembled, a

single sandwich (FIGURE 3). The airgaps are thelf;

aligned along the axis 17, the uprights 1411,1411, 14c

overlap over a portion of their surface, and 'the windings 16a, 16b, Inc-are situated outside the said sandwich as clearly shown in FIGURE 5, the windings of the even transducersbeing aligned on one sidejand those of the odd transducers on the other side .of the uprights 14a,

It will be seen an FIGURES .that,' by reas n of this arrangement, a gap equal to the thickness of one transv ducer is available'between the limbs (15a, 15c) of the transducer elements of like parity to'receive the windings (16a',-16c). i g V I Thernultiple head according to the invention may com-- prise-in-addition members such as 18 (FIGURE 5) separating the various magnetic circuits.- 'ljhese members,-

which are endowed with appropriate properties, can perform a complementary =funct-ionin the operation of the multiple head. They may serve also to reduce the Wear on the-magnetic circuits at the level of the air gap; and to support the output terminals of the windings.

Forthe sake, of

FIGURE 6 is similar to FIGURE 4, but thema'gnetic a eircuitstherein are shown. without their windings] clarity, such membershave notbeen -illustrated in FIGURES 2, 3. and 4of the drawings.

and 1600f In the magnetic circuit 11a, the various parts which will hereinafter be defined are denoted :by Ba, D11, Aa, Ca and B'a. Homologous parts of the circuits 11b and 11c will be denoted by the same capital letters B, D, A, C, B together with the indices b and respectively.

The parts Aa, Ba, B'a of the circuit 11:: are those which overlap some parts of the adjacent circuit llb and are consequently separated by the latter from the following circuit of like parity (11c of FIGURE 3).

The parts Ca and Da are those which are not separated from the circuit of like parity (11c, FIGURE 3) by the adjacent circuit 11b.

The opposing parts Aa and Ab, Ba and Bb, and 8'5; and Bb of the adjacent circuits determine leakage permeances PA, P and P between these circuits being identical to P and the opposing parts Ca and Cc, and Da and Dc of the successive circuits of like parity determine leakage permeances P and P between circuits of like parity.

In the following, no account will be taken of the permeances P When a magnetomotive force is applied to the air gap in the magnetic circuit 11a, it may be considered in the first place that there is a main leakage tiux in the circuit consisting of: the part B'a of the circuit 111.2, the permeance P (identical to P between the adjacent parts B'a, and Bb, the parts Bb, Db and Ab of the adjacent circuit 11b, the permeance P between the adjacent parts Ab and'Aa and the parts Aa, Da, Ba of the circuit 11a. It will therefore be seen that the circuit of the stray flux considered is closed by the parts Bb, Db, Ab of the adjacent circuit 11b, but not by the limb 15b of the circuit supporting the winding. Owing to this arrangement of the invention, crosstalk between adjacent transducers is substantially reduced. A closer study of the various stray fiuxesindicates that the crosstalk between adjacent transducers varies in the same sense as the permeance P and inversely to the permeance P and that the crosstalk between transducers of like parity varies in the same 1 sense as the permeances P P and P These results have been experimentally confirmed.

Therefore, the crosstalk between adjacent transducers is reducedby 'increasing the permeance P 5, but the crosstalk between transducers of like parity is then increased. This crosstalkphowever, remains low if the permeances P and P are'themselves low, and it is lower than the crosstalk between adjacent heads.

3 In practice, in order to reduce crosstalk both between adjacent transducers and between transducers of like parity of a multiple head according to the invention, it willbe advantageous to increase the permeance P and to reduce the permeances 'P and P contour of the magnetic circuits may be so chosen that For this reason, the

the rati'o of the areas A-to the areas and to the areas C is as. large as possible.

. Inthe embodiment of the invention as illustrated in FIGURE 7,-the part 14 of the magnetic circuit has been so modified as to overlap the limb 15 of the adjacent transducers only in the immediate neighbourhood of the air gap, so that'the overlap areas B (and B) and consequently the permeancesP are extremely small.

In order to increase the permeances P the space situated' between the parts A of the adjacent circuits will ad vantageouslybe 'filled with magnetic material. For example, this efie'ctmay be produced by increasing the thickness of the parts A themselves.

' The inventionis not limited to a multiple magnetic j head consisting of like transducers or of transducers comprising-windings arranged in like manner.

For example, it will be seen in FIGURE 8 that the limbs ISa'and 15c of the successive transducers of like parity may be disposed at dilTerent-distances from the uprights.

14a and 14c, and from FIGURE 9 that the windings 16a two successive transducers of like parityrnay be differently positioned' on the transducers;

This makes it possible to leave more space for the windings and to modify the permeances P An importance application of the inventive idea consists in providing a lateral extension 114 (FIGURES 10 and 11) on the uprights 14 of the magnetic circuits, so that the portions C of the limbs 15 are separated from the transducers of like parity by this extension. If then the regions C1 and C2 respectively above and below the windings 16 in the parts C in FIGURE 10 are considered, it will be seen that the leakage permeances P1 and P2 existing between these regions C1 and C2 and the extensions 114 of an adjacent circuit are in parallel with the previously defined permeances P and P respectively. All the stray fluxes of any appreciable value in each transducer are therefore closed through the uprights 1d and the extensions 114 of the adjacent transducers without passing through the succeeding transducers, so that the crosstalk between transducers of like parity is substantially eliminated.

The screens illustrated at 29 in FIGURES l0 and 11 may be formed in two parts 21 and 22 situated in a common plane and separated by the lines 23, 24, 25, 26. These parts may consist of different materials.

ther arrangements and other forms of the elements of a multiple head may be envisaged within the scope of the invention.

Laminated or compressed powder materials may noturally be employed to form the magnetic members.

The uprights 14 of the transducers may consist, at least partially, of members of magnetic material common to the various transducers.

All the magnetic circuits may be integrally formed, their uprights 14 then forming a single block.

Multiple magnetic heads according to the invention are particularly applicable to the direct reading of char acters printed in magnetic ink on cheques. The invention makes it possible to provide multiple heads comprising 1t) juxtaposed transducers over a width of 3 millimetres, which corresponds to the height of the numerals thus printed. The windings of the various transducers are then individually connected to amplifiers, the outputs of which supply signals to a decoding device.

" I claim:

1. A multiple magnetic head comprising a plurality of identical fiat electromagnetic transducers each includ tangular plate provided with a substantial triangular inner aperture, one side of said aperture being parallel to and near one of the short sides of the rectangular plate, a first leg of said core being defined between these parallel sides, and the apex of said triangular aperture opposite said one side thereof being close to the middle of one of the long sides of said rectangular plate, a second leg of said core being defined between a second side of said aperture and the second one of the short sides of the rectangular plate, said plate being further provided with a slit perpendicular to said long side joining said side to said apex and forming a Working air gap in said core, each of said transducers further including a coil carried by said first leg of the core, and said transducers being assembled side by side With their air gaps in alignment within a common plane and with coils of adjacent transducers on opposite sides of said common plane, the sec-, ond leg of the core of each transducer overlapping large 4 portions of the second leg of adjacent cores.

3. A multiple magnetic head comprising a plurality.

metrical with respect to said plane, said plate being pro- I vided with a triangular inner aperture located on one side of said plane, an apex of said aperture lying in said along this side of the aperture which is opposite said apex, forming a leg of thecore which carries the coil of the transducer, the cores of the several transducers being of the same size and said transducers being assembled side by side with their air gaps in alignment within a common plane and with coils of adjacent transducers on opposite sides of said common plane.

References Iited by the Examiner UNlTED STATES PATENTS 2,732,275 1/56 MacNeill 179100.2 2,784,259 3/57 Camras 179100.2 2,807,676 9/57 Lynn 179- -100.2 2,840,643 6/58 Brower 179100.2 2,872,530 2/59 Jolly 179--100.2

10 IRVING L. SRAG-OW, Primary Examiner. 

1. A MULTIPLE MAGNETIC HEAD COMPRISING A PLURALITY OF IDENTICAL FLAT ELECTROMAGNETIC TRANSDUCERS EACH INCLUDING A MAGNETIC CORE HAVING THE GENERAL SHAPE OF A RECTANGULAR PLATE PROVIDED WITH A SUBSTANTIAL TRIANGULAR INNER APERTURE, ONE SIDE OF SAID APERTURE BEING PARALLEL TO AND NEAR ONE OF THE SHORT SIDES OF THE RECTANGULAR PLATE, A FIRST LEG OF SAID CORE BEING DEFINED BETWEEN THESE PARALLEL SIDES, AND THE APEX OF SAID TRIANGULAR APERTURE OPPOSITE SAID ONE SIDE THEREOF BEING CLOSE TO THE MIDDLE OF ONE OF THE LONG SIDES OF SAID RECTANGULAR PLATE, A SECOND LEG OF SAID CORE BEING DEFINED BETWEEN A SECOND SIDE OF SAID APERTURE AND THE SECOND ONE OF THE SH ORT SIDES OF THE RECTANGULAR PLATE, SAID PLATE BEING FURTHER PROVIDED WITH A SLIT PERPENDICULAR TO SAID LONG SIDE JOINING SAID SIDE TO SAID APEX AND FORMING A WORKING AIR GAP IN SAID CORE, EACH OF SAID TRANSDUCERS FURTHER INCLUDING A COIL CARRIED BY SAID FIRST LEG OF THE CORE, AND SAID TRANDUCERS BEING ASSEMBLED SIDE BY SIDE WITH THEIR AIR GAPS IN ALIGNMENT WITHIN A COMMON PLANE AND WITH COILS OF ADJACENT TRANSDUCERS ON OPPOSITE SIDES OF SAID COMMON PLANE, THE SECOND LEG OF THE CORE OF EACH TRANSDUCER OVERLAPPING LARGE PORTIONS OF THE SECOND LEG OF ADJACENT CORES. 